Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$247.39	13.256%	$280.184	$280.18	$280.20	$280.20
Purchase #2	$72.57	12.250%	$81.4598	$81.46	$81.45	$81.50
Purchase #3	$84.75	9.522%	$92.8199	$92.82	$92.80	$92.80
Purchase #4	$35.81	4.700%	$37.4931	$37.49	$37.50	$37.50
Purchase #5	$212.39	11.618%	$237.0655	$237.07	$237.05	$237.10
Purchase #6	$44.83	5.839%	$47.4476	$47.45	$47.45	$47.40
Purchase #7	$145.66	4.773%	$152.6124	$152.61	$152.60	$152.60
7 purchase totals =	$843.40		$929.0823	$929.08	$929.05	$929.10